Development of a new coolant mass estimation method for PWR accidents; Effectiveness of primary loop level meters designed for a PWR

Suzuki, Mitsuhiro

A new method to estimate almost all coolant mass change during a loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR) was developed as an important technique for accident management (AM) measures. An AM action to inject water into a PWR is required by a key parameter of core exit thermocouples (CETs) in many OECD countries but by a reactor vessel level meter in a few countries. It is obvious that the CETs can give no information on the primary coolant mass change but indication of core heat-up. The new method uses the primary loop (PL) level meters designed to measure water level in each steam generator (SG) outlet region, and the reactor vessel level indication system (RVLIS) in the Westinghouse-type PWR in addition to the pressurizer level meter. The author clarified through the ROSA/LSTF experiments that these three kinds of level meters are useful to estimate more than 80% of the total coolant mass change between the initial and core heat-up conditions. It is important to understand the role of PL level meters which almost cover an insensitive coolant mass detection range of the RVLIS before the core heat-up initiation.